During recent decades, ultrasonic technology has played an ever-increasing role in examining the internal structure of living organisms. The technology employed has applications in diagnosis of various medical ailments where it is useful to examine soft tissues within the body which shows structural details such as organs and blood flow. This enables medical staff to locate the portions which may indicate that disease or abnormalities are present. To examine the internal body structure, ultrasonic images are formed by producing ultrasonic waves using a transducer, passing the waves through a body, and measuring the properties of the scattered echoes (i.e., amplitude) from reflections inside the body using a receptor.
More recently, these imaging systems also detect velocity along the axis of the interrogating sound beam, along with the amplitude. Such detection can provide an image of the blood flow pattern or vessel network, which is information of high diagnostic significance. The detection of velocity is based upon the Doppler principle, whereby a change in observed frequency of the reflected echo pulse indicates a corresponding change in velocity has occurred in the region from which the echo emanates.
The conventional ultrasonic imaging apparatus is shown in block .diagram format as ultrasound imager 100 in FIG. 1. Referring to FIG. 1, front end processor 101 is coupled to demodulator 102. The output of demodulator 102 is coupled to display processor 103. Front end processor 101 typically includes a linear array, an annular array, and a single crystal probe with an analog or digital beam former. Front end processor 101 recurrently sends and receives ultrasonic waves into a body. Front end processor 101 produces modulated signals representing the data obtained from receiving the echoes that occurred within the body. Demodulator 102 receives the signal from front end processor 101 and produces the phase and amplitude information, having the characteristic of tissue and Doppler echo. In the prior art, the phase information is not utilized for any specific purpose for the B-scan images. Thus, in the prior art, the signals are only subjected to magnitude detection for displaying ultrasound B-scan images..The amplitude information generated from the magnitude detection would be output to display processor 103. Processor 103 would display images consisting of magnitude cluster from the signal. Phase information is used in ultrasound Doppler images. These Doppler images consist of overlapping multiple signals and determining the phase differences between the multiple signals. Phase information is not generated and displayed which depicts the phase difference between different parts of the same signal.
In the prior art, the baseband signal from front end processor 101 is demodulated using analog techniques. For instance, a full-wave or half-wave rectifier followed by a low pass filter would remove the carrier frequency utilized to modulate the signal. This technique, though good for amplitude modulation (A.M.) radio receivers, is not generally acceptable for ultrasound machines. Another analog technique uses the quadrature demodulator. In a quadrature demodulation system, a mixer is used to shift the RF frequency down to the baseband in order to extract the Doppler phase shift. In reality, the harmonic distortion, channel mismatching, component variation, etc., limit the performance and make it difficult to manufacture the system. Other analog techniques include squaring and peak detection. Even though these are viable techniques today, higher resolution B-scan image and sensitive Doppler information are becoming requirements for the next generation ultrasound machines. To achieve these results, a wide bandwidth and wide dynamic range signals must be processed because the echo from the body is considered as a wide band amplitude and phase modulated signal.
The prior art analog techniques do not adequately accommodate the wide band amplitude and phase modulated signals. Furthermore, the analog approaches have difficulty maintaining consistency from machine to machine and lack flexibility to accommodate requirements changes, as illustrated above.
The present invention allows for demodulation in ultrasound instruments. By providing a digital approach, reliability and consistency are improved. The present invention accommodates wide bandwidth and wide dynamic range signals. Furthermore, the present invention utilizes display and detection of phase information in ultrasound B-scan image.